split lines the same when read from stdin

4 files changed, 47 insertions, 29 deletions

diff --git a/src/flake8/processor.py b/src/flake8/processor.py
index 498b9c7..aa7f1d8 100644
--- a/src/flake8/processor.py
+++ b/src/flake8/processor.py
@@ -334,7 +334,7 @@ class FileProcessor(object):
     def read_lines_from_stdin(self):
         # type: () -> List[str]
         """Read the lines from standard in."""
-        return utils.stdin_get_value().splitlines(True)
+        return utils.stdin_get_lines()
 
     def should_ignore_file(self):
         # type: () -> bool
diff --git a/src/flake8/utils.py b/src/flake8/utils.py
index 5c7232c..29df9bc 100644
--- a/src/flake8/utils.py
+++ b/src/flake8/utils.py
@@ -13,6 +13,7 @@ from typing import Callable, Dict, Generator, List, Optional, Pattern
 from typing import Sequence, Set, Tuple, Union
 
 from flake8 import exceptions
+from flake8._compat import lru_cache
 
 if False:  # `typing.TYPE_CHECKING` was introduced in 3.5.2
     from flake8.plugins.manager import Plugin
@@ -189,28 +190,31 @@ def normalize_path(path, parent=os.curdir):
     return path.rstrip(separator + alternate_separator)
 
 
-def _stdin_get_value_py3():  # type: () -> io.StringIO
+def _stdin_get_value_py3():  # type: () -> str
     stdin_value = sys.stdin.buffer.read()
     fd = io.BytesIO(stdin_value)
     try:
-        (coding, lines) = tokenize.detect_encoding(fd.readline)
-        return io.StringIO(stdin_value.decode(coding))
+        coding, _ = tokenize.detect_encoding(fd.readline)
+        return stdin_value.decode(coding)
     except (LookupError, SyntaxError, UnicodeError):
-        return io.StringIO(stdin_value.decode("utf-8"))
+        return stdin_value.decode("utf-8")
 
 
-def stdin_get_value():
-    # type: () -> str
+@lru_cache(maxsize=1)
+def stdin_get_value():  # type: () -> str
     """Get and cache it so plugins can use it."""
-    cached_value = getattr(stdin_get_value, "cached_stdin", None)
-    if cached_value is None:
-        if sys.version_info < (3, 0):
-            stdin_value = io.BytesIO(sys.stdin.read())
-        else:
-            stdin_value = _stdin_get_value_py3()
-        stdin_get_value.cached_stdin = stdin_value  # type: ignore
-        cached_value = stdin_get_value.cached_stdin  # type: ignore
-    return cached_value.getvalue()
+    if sys.version_info < (3,):
+        return sys.stdin.read()
+    else:
+        return _stdin_get_value_py3()
+
+
+def stdin_get_lines():  # type: () -> List[str]
+    """Return lines of stdin split according to file splitting."""
+    if sys.version_info < (3,):
+        return list(io.BytesIO(stdin_get_value()))
+    else:
+        return list(io.StringIO(stdin_get_value()))
 
 
 def parse_unified_diff(diff=None):
diff --git a/tests/integration/test_main.py b/tests/integration/test_main.py
index 42ad76c..9193071 100644
--- a/tests/integration/test_main.py
+++ b/tests/integration/test_main.py
@@ -51,6 +51,29 @@ index d64ac39..7d943de 100644
     assert err == ''
 
 
+def test_form_feed_line_split(tmpdir, capsys):
+    """Test that form feed is treated the same for stdin."""
+    src = 'x=1\n\f\ny=1\n'
+    expected_out = '''\
+t.py:1:2: E225 missing whitespace around operator
+t.py:3:2: E225 missing whitespace around operator
+'''
+
+    with tmpdir.as_cwd():
+        tmpdir.join('t.py').write(src)
+
+        with mock.patch.object(utils, 'stdin_get_value', return_value=src):
+            _call_main(['-', '--stdin-display-name=t.py'], retv=1)
+            out, err = capsys.readouterr()
+            assert out == expected_out
+            assert err == ''
+
+        _call_main(['t.py'], retv=1)
+        out, err = capsys.readouterr()
+        assert out == expected_out
+        assert err == ''
+
+
 def test_e101_indent_char_does_not_reset(tmpdir, capsys):
     """Ensure that E101 with an existing indent_char does not reset it."""
     t_py_contents = """\
diff --git a/tests/unit/test_file_processor.py b/tests/unit/test_file_processor.py
index f38568c..e5367a8 100644
--- a/tests/unit/test_file_processor.py
+++ b/tests/unit/test_file_processor.py
@@ -89,20 +89,15 @@ def test_should_ignore_file_to_handle_disable_noqa(default_options):
 @mock.patch('flake8.utils.stdin_get_value')
 def test_read_lines_from_stdin(stdin_get_value, default_options):
     """Verify that we use our own utility function to retrieve stdin."""
-    stdin_value = mock.Mock()
-    stdin_value.splitlines.return_value = []
-    stdin_get_value.return_value = stdin_value
+    stdin_get_value.return_value = ''
     processor.FileProcessor('-', default_options)
     stdin_get_value.assert_called_once_with()
-    stdin_value.splitlines.assert_called_once_with(True)
 
 
 @mock.patch('flake8.utils.stdin_get_value')
 def test_stdin_filename_attribute(stdin_get_value, default_options):
     """Verify that we update the filename attribute."""
-    stdin_value = mock.Mock()
-    stdin_value.splitlines.return_value = []
-    stdin_get_value.return_value = stdin_value
+    stdin_get_value.return_value = ''
     file_processor = processor.FileProcessor('-', default_options)
     assert file_processor.filename == 'stdin'
 
@@ -111,9 +106,7 @@ def test_stdin_filename_attribute(stdin_get_value, default_options):
 def test_read_lines_uses_display_name(stdin_get_value, default_options):
     """Verify that when processing stdin we use a display name if present."""
     default_options.stdin_display_name = 'display_name.py'
-    stdin_value = mock.Mock()
-    stdin_value.splitlines.return_value = []
-    stdin_get_value.return_value = stdin_value
+    stdin_get_value.return_value = ''
     file_processor = processor.FileProcessor('-', default_options)
     assert file_processor.filename == 'display_name.py'
 
@@ -123,9 +116,7 @@ def test_read_lines_ignores_empty_display_name(
         stdin_get_value, default_options,
 ):
     """Verify that when processing stdin we use a display name if present."""
-    stdin_value = mock.Mock()
-    stdin_value.splitlines.return_value = []
-    stdin_get_value.return_value = stdin_value
+    stdin_get_value.return_value = ''
     default_options.stdin_display_name = ''
     file_processor = processor.FileProcessor('-', default_options)
     assert file_processor.filename == 'stdin'